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Wots Wot Foam E Side Thrust?


Edgeflyer
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Does anyone know whether side thrust or even down thrust is needed on this model? I noticed mine wants to roll right slightly on increasing throttle. The motor mount has a packing under the left side to push the motor right. Is this helpful or best removed?

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Increasing power suddenly   ( if the prop turns clockwise from behind as usual)    gives a left movement due to inertia from the prop and spiral airflow on the fuse and rudder, that is why the motor is usually canted to the right to help cancel this out. My sons Foam E performs perfectly straight out of the box as standard. The only reason I can think of is if your motor turns anti clockwise

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On 31/07/2022 at 08:54, Phil B said:

Does anyone know whether side thrust or even down thrust is needed on this model? I noticed mine wants to roll right slightly on increasing throttle. The motor mount has a packing under the left side to push the motor right. Is this helpful or best removed?

Hi Phil

 

A couple of questions first.  Is this model new and straight out of the box to you or is it second hand?  Is the rudder at neutral perfectly aligned with the fin?

 

Application of rudder on a Wots Wot, or Wot 4 or Acro Wot, produces a very strong rolling effect as all the rudder is above the motor thrust line.  If you have a slightly warped fuselage or twisted fin, you may have added so rudder trim to fly straight.  This will only work for one airspeed as the rudder effect is speed dependent - actually dependent on speed squared.

 

Back to the motor.  To check motor and side and down thrust, make sure you trim the aircraft to fly straight and level at your chosen cruise speed.  By that I mean, take your hands off the sticks and check that it flies in the straight line and flies level.  Use aileron trim to eliminate any rolling effect and elevator trim to get it to fly level.  Then, pull up to a vertical climb smoothly applying full power and check if the aircraft pulls to the left (more right thrust needed) or pulls to the right (less side thrust needed).

 

If you cannot adjust the engine side and down thrust, you will have to resort to the other, but not as effective technique, of mixing rudder and/or elevator to keep the aircraft flying level and straight as you open the throttle.  Again, don't just slam the throttle open as you will get transient effects that the mix will not cope with.  It is better to alter the motor side and down thrust to achieve this as that will hold true for almost all airspeeds whereas a mix will only really work for one airspeed and be sub optimal at all other air speeds.

 

Hope that helps.

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On 31/07/2022 at 08:54, Phil B said:

Does anyone know whether side thrust or even down thrust is needed on this model? I noticed mine wants to roll right slightly on increasing throttle. The motor mount has a packing under the left side to push the motor right. Is this helpful or best removed?

 

Short answer - flies beautifully as it comes out of the box..... if it has a shim, leave it in place.

 

It isn't, nor will it ever be, a precision aerobat, so be prepared to use all 4 controls manually - or spend months chasing your tail with multiple mixes or manual adjustments.

 

In my view this is, by far, the best Foss Foamie......

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23 hours ago, Peter Jenkins said:

Application of rudder on a Wots Wot, or Wot 4 or Acro Wot, produces a very strong rolling effect as all the rudder is above the motor thrust line.  If you have a slightly warped fuselage or twisted fin, you may have added so rudder trim to fly straight.  This will only work for one airspeed as the rudder effect is speed dependent - actually dependent on speed squared.

AFAICS from pics of the Wots Wot the motor thrust line is pretty much central to the rudder area, certainly wouldn't create much, if any, rolling effect. 

The varying airspeed effect of the rudder will be similar to varying the throttle with side thrust. 

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I've flown quite a few WotsWots and have had one as a winter hack for a few years (having the battery hatch on the top makes it much easier for muddy field operation than the other foamy Wots). As with others I found all of them flew well straight out of the box. 

 

However flying mine one calm afternoon I decided to play about with mixing to produce apparent pure yaw from the rudder. I ended up with 15% opposite aileron mix and 30% up elevator mix (with a baseline max travel ailerons 80%, and elevator max travel 125% up & 65% down). With this the model wags from side to side with the application of rudder but continues straight and level. Note I'm not advocating that anyone else does this rather, as GG says, just enjoy it for Wot it is.

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Just been and had a look at my Wots Wot - admittedly its the IC version - and approximately 80% of the rudder is above the thrust line.  Application of rudder produces and almost instant roll in the direction of rudder - secondary effect of rudder but the immediacy of the roll is because of the rolling moment applied by having 80% of the rudder above the thrust line.  The Wot 4 has over 90% of the rudder above the thrust line.

 

If you try and fly an axial roll using rudder on a Wots Wot, you have a really difficult task.  Say you are rolling right, as the aircraft begins the roll, you need to introduce increasing amounts of left rudder.  The secondary effect of this is to introduce a force trying to roll the aircraft to the left the effect of which is so the roll rate to the right to slow down.  The most left rudder is reached as the wings reach 90 degs and then you feed off left rudder and feed in down elevator.  The roll rate now increases as the left roll force induced by left rudder reduces. As the aircraft passes thought inverted you need to start applying right rudder as well as reducing down elevator.  The effect of applying right rudder is to introduce a force to roll the aircraft to the right and that adds to your existing right roll command resulting in the roll rate speeding up.   If, as John Lee has done you introduce a mix so that when say left rudder is applied a small amount of right aileron is introduced so that as he found you can just get yaw.  You can also go to the second mix he mentioned of adjusting the elevator using a rudder controlled mix to maintain a level flight path when rudder is used.  

 

If you do that your ability to roll axially at a constant roll rate becomes very much easier.  There is also the issue of getting the CG to an optimal position for the aircraft.  The CG specified isn't always in the optimal position.  Experiment by moving the drive battery, if that is possible, so that you can ease the CG back to see how it improves handling.

 

I had my Wot 4 trimmed out for doing my B and a friend asked if he could fly it to compare it with his.  He was astonished and said it was like flying a completely different aircraft and asked if I could set his up to fly in the same way.  This I did and he was a very happy bunny.

 

If you think this level of attention to trimming your aircraft is not worth it, then so be it.  If you do try it, you will be rewarded with an aircraft that will fly so much better and allow you to concentrate on flying manoeuvres rather than just flying as you are using a lot of effort to overcome aircraft characteristics.  

 

Yes, I fly F3A aerobatics with a 2 mtr class aircraft.  When I put complete beginners on it, using a buddy box of course(!), they find it very easy to fly as it has no bad habits.  A couple of guys with A Certificates had a go with it as well and commented that it was so much easier to fly than their model.  They also commented that the amount of control throw was very low and they felt uncomfortable that they might not have enough elevator throw if they screwed up.  That's a different matter but less control throw is almost always helpful in improving the accuracy with which you can fly your aircraft.  I have my Wots Wot set up in this way and it flies like it's on rails.

 

You choice - just saying.

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Purely personal choice of course.

 

Mine was to take it out of the box and just fly it 1000 times - I smile every time.  The challenge of balancing controls to do an even semi passable knife edge is still there.  It's got foibles and habits (not bad habits) but they just add to it's appeal for me.  That it doesn't do perfectly axial rolls, or does not have 'pure' yaw control doesn't make it bad to fly...... (i'm not convinced that adding mixes will work at all airspeeds tbh - they must help, but not mix out all unintended coupling at all speeds - unless throttle is included in every mix).

 

I's trimmed enough for me to enjoy it and to do reasonable aerobatics.  No everyone wants every plane to behave like a pattern plane.

 

Back to the OP - there is no need to remove the shim.

Edited by GrumpyGnome
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Mixes only work completely at one airspeed - what we call the datum airspeed.  You also cannot turn a sows ear into a silk purse - not that I think the Wots Wot is a sows ear - it's just a saying.  

 

You are perfectly entitled to say just go and fly the thing but the OP was looking for help in overcoming some of the short comings of the design and set up.  Just saying - go fly it 1,000 times - is not particularly helpful as an answer IMHO.  I've tried to provide some answers and so have some others.  So, at least the OP can decide which route to take.

 

Good luck with whichever route is taken!

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